Currently available cutters include a PCD layer or table supported by or joined coherently to a substrate, post, or stud that is frequently made of tungsten carbide. Bonding the diamond layer to the substrate generally occurs during high pressures high temperature sintering (HPHT). Typically, a sintered PCD material comprises diamond particles with extensive amounts of direct diamond-to-diamond bonding as the major phase. The diamond particles also include interstices wherein a binder phase resides.
The binder phase can also be referred to as the binder, metal phase or the catalyst solvent phase. The binder phase forms a network intermingled with the diamond network and typically includes at least one metal, or a combination of metals, selected from cobalt (Co), nickel (Ni), and iron (Fe). During sintering, the binder phase sweeps the diamond particles and assists in the formation of diamond-to-diamond bonds by the well-known liquid sintering mechanism of solution-transportation-reprecipitation.
Although the binder phase greatly assists in the formation of the desired diamond-to-diamond bonds in PCD materials, the presence of the binder phase can be detrimental to the performance of a cutting bit prepared from the resultant PCD. For example, PCD cutters are subjected to large sustained forces for a long period of time. These sustained forces result in the generation of substantial heat which can cause failure of the PCD cutter in a variety of ways.
For example, in certain circumstances, the PCD material can graphitize in the presence of the binder phase, resulting in the loss of diamond-to-diamond bonds. The loss in diamond-to-diamond bonding results in a volume change which subsequently causes the PCD to wear faster. In other circumstances, the heat generated during cutting, drilling, or mining exacerbates differences in the thermal expansion coefficients between the diamond phase and the binder phase. This mismatch between the binder phase and the diamond phase can cause microcracking in the diamond phase as the binder phase expands to a greater extent than the surrounding diamond. As with graphitization, microcracking causes the PCD cutter to wear faster.
Although some have attempted to address this problem, the processes known in the art tend to be cumbersome and require multiple steps. For example, WO 2008/063568 discloses, amongst other processes, a two-step process for enhancing the stability of PCD materials. The process disclosed in WO 2008/063568 involves preparing a PCD material using known processes, subsequently leaching the binder phase out of the PCD using an acid bath (aqua-regia), and finally treating the leached PCD material under appropriate temperature and pressure with Si or an Si containing material to produce a silicon carbide bonded PCD substrate.
WO 2008/063568 further discloses methods involving the apparent simultaneous HPHT treatment of diamond particles with molten Co and Si or an Si containing material.
While these various procedures are alleged to result in the formation PCD materials having enhanced properties, the aqua-regia procedure requires two distinct steps. Likewise, due to the lower melting point of some silicon compounds, a molten Co/Si process allows mixing of Co and Si material before the diamond is sintered. Thus, what is needed is a single step process that prevents the mixing of Co and Si materials before the diamond is sintered, but subsequently allows Si to diffuse or sweep or mix with the cobalt, so that the performance of the resulting material is enhanced.